Effect Of Thermo-treatment On Properties Of Bamboo-based Fiber Composites

Bamboo-based fiber composites (BFC) are made from bamboo fibrous veneers, which arethe basic element and hot (cold) pressed in long grain direction. In this technology, not only thelarge-diameter bamboo but also the trails class miscellaneous bamboo can be used, andbamboo utilization rate is above90%. The BFC can be designed broadly, it can be used formanufacturing wind power blade, vessel deck, container floor and construction support woodand so on, and also can be used as an indoor decoration and decorating materials, highweathering resistance outdoor materials, its application prospects is broadly. In recent years,thermo-treatment in bamboo has been widely used in Chinese bamboo enterprises with theincreasing different color needs for people in bamboo products. While, the demand for indoorand outdoor BFC is also increasing. Study on the properties of BFC after thermo-treatment hasa great role in the promotion for the expansion of BFC applications, it also can enhance theoverall competitiveness in BFC industry, and has a significant improve for added value.In this paper, Phyllostachys pubescens bamboo, Neosinocalamus affinis bamboo, andPhyllostachys iridescens bamboo were used as the main raw material. The bamboo fibrousveneers were thermo-treated in superheated steam with different steam pressure (0.35MPa、0.40MPa and0.45MPa) and duration(110min、140min and170min). Then the bamboo fibrousveneers were reconstituted with phenol-formaldehyde adhesive and hot pressing process forBFC. The morphology of the bamboo fibrous veneers and the damage of cell wall wereanalyzed by scanning electron microscopy, and the effect of thermo-treatment on them wasalso studied. The effect of thermo-treatment on the chemical properties of bamboo fibrousveneers and the physical and mechanical properties of BFC was studied. The main results weresummarized as follows:(1) The effect of thermo-treatment on the morphology of bamboo fibrous veneers was notsignificant. However, bamboo fibrous veneers became crisp after heat-treated at hightemperature, the waxy layer was removed much more than untreated bamboo, but no significant difference was found for outside bamboo. The starch granules in the parenchymacells were many for untreated bamboo, but the quantity reduced significantly afterthermo-treatment, and the particles became smaller. There were little changes in the cell wallafter thermo-treatment.(2) For the three bamboo species, the holocellulose and α-cellulose contents ofNeosinocalamus affinis bamboo were the largest, but the difference in the contents ofholocellulose and α-cellulose of Phyllostachys pubescens bamboo and Phyllostachys iridescensbamboo was little. For Phyllostachys pubescens bamboo and Neosinocalamus affinis bamboo,the contents of holocellulose and α-cellulose reduced significantly after thermo-treatment.While, the holocellulose content of Phyllostachys iridescens bamboo decreased significantlyafter thermo-treatment, but the α-cellulose content increased compared with control samples.The effect of thermo-treatment on different kind’s bamboo were different, due to the differentstructure of the different bamboo species.The decrease in hemicellulose content was largest, and the hemicellulose contentdecreased with the higher steam pressure and longer treatment duration.After thermo-treatment, the water extractives contents of bamboo increased significantly,the biggest increase was for Neosinocalamus affinis bamboo, and followed by Phyllostachyspubescens bamboo.The pH value reduced significantly after thermo-treatment, the largestreduction was for Neosinocalamus affinis bamboo. However, the effects of steam pressure andduration on pH value were not significant.The total buffering capacity increased significantly after thermo-treatment. ForPhyllostachys pubescens bamboo, the total buffering capacity increased with longer duration,but it decreased for Neosinocalamus affinis bamboo. For Phyllostachys iridescens bamboo, itincreased first and then decreased with longer duration. While the total buffering capacity ofPhyllostachys pubescens bamboo and Phyllostachys iridescens bamboo decreased with highersteam pressure, but for Neosinocalamus affinis bamboo, the value was first increased and thendecreased. (3) In the process of making bamboo-based fiber composites, the press closing timedecreased significantly when the bamboo fibrous veneers after thermo-treatment.The compression of cell walls were analyzed through scanning electron microscopy, thesmaller degree compression of the catheter, thin-walled cells near the outside bamboo, and thegreater degree compression of the catheter, thin-walled cells near the inside bamboo. The BFCmade from the bamboo fibrous veneers after thermo-treatment had bigger compression degreecompared with untreated samples.(4) The lightness and b*of bamboo fibrous veneers decreased significantly afterthermo-treatment, while a*increased. The total color difference increased gradually asincreasing steam pressure and duration. Due to the difference in chemical composition betweendifferent bamboo species, the degree of color change was different under the samethermo-treatment conditions.(5) The color of BFC made from the bamboo fibrous veneers after thermo-treatmentbecame deeper, and the color was brick red. The total color of the three bamboo speciesincreased with increasing steam pressure and duration.The color change of BFC made from the untreated bamboo fibrous veneers mainly due tothe color of PF. While, the lightness change of BFC made from the bamboo fibrous veneersafter thermo-treatment mainly due to the color of PF, but the effects of PF on a*and b*werelittle. After hot pressing, the lightness of BFC increased compared with the bamboo fibrousveneers which glued, but a*and b*were little affected.(6) After thermo-treatment, the thickness swelling rate and width swelling rate of BFCreduced significantly compared with control samples. This was mainly due to the degradationin hemicellulose of bamboo.(7) After thermo-treatment, the bending strength (MOR) of BFC of three bamboo speciesdecreased with increasing steam pressure and duration.For Phyllostachys pubescens bamboo, the modulus of elasticity (MOE) of BFC changedlittle after thermo-treatment. For Neosinocalamus affinis bamboo, the MOE increased whenheat-treated at0.40MPa for110min~170min, while, the MOE increased first and then decreased when treated at0.35MPa~0.45MPa for140min. For Phyllostachys iridescensbamboo, the MOE increased after thermo-treatment, but the difference was not significant.For Phyllostachys pubescens bamboo, the Horizontal shear strength (HS) of BFCdecreased with increasing steam pressure and treatment duration. For Neosinocalamus affinisbamboo and Phyllostachys iridescens bamboo, the HS showed a trend of increased, especiallyfor Phyllostachys iridescens bamboo, the HS increased significantly after thermo-treatment,only decreased significantly when heat-treated at0.45MPa for140min.